This invention relates generally to improvements in rupture disk pressure relief devices of the type which when activated must contain the discharge within a discharge piping system. In addition, the invention pertains to novel methods of manufacturing rupture disks to achieve reliability and predictability in the finished product. In particular, the improvements address and favorably resolve the tendency for these types of devices to leak or change setpoint due to stresses imposed upon them during installation and service. In addition, by reason of the use of a novel method of heat sinking during welding or brazing the components together, the rupture disk assemblies avoid all internal thermal stresses arising from welding or brazing.
Rupture disks devices are non-reclosing pressure relief devices intended to prevent catastrophic overpressure inside of a pressure vessel, and safely channel any discharge within a discharge piping system. They typically comprise a two-piece tubular body sealed against internal flow by a disk, usually convex when viewed from the high pressure side, designed to rupture at a predetermined pressure. The bodies are designed to connect to a discharge piping system. The piping system is designed to transport the highly pressurized product, either liquid or gas, to a protected vessel in a safe discharge location.
At levels below the safe working pressure of protected vessels, rupture disks are designed to remain sealed, allowing no leaks out of or through the discharge piping. If the pressure in the protected vessels reach a carefully predetermined point, the rupture disk devices are designed so as to rupture, allowing flow through the discharge piping, without allowing leakage to the outside of the piping.
In heretofore known rupture disk designs, the sealing of the disk, the sealing of the body from leaks outside the piping system, and the stability of the disk rupture pressure is at least to some degree affected by external forces on the rupture disk device.
In some designs the external forces are mechanical loads, particularly uneven loads, generated by bolts or threading required to assemble and seal the device. Careful control of assembly torque is required in order not to influence the sealing or burst point. Other rupture disk devices are affected by stresses induced by the discharge piping. The piping stress is transferred directly to the disk, and mounting of the disk affects both sealing and burst pressure. While these external forces are expected, they are in practice difficult to control or compensate for with exactitude. As a result, the sealing integrity and burst pressure integrity of previous designs are compromised by these external forces.
In view of the failure of the prior art to develop rupture disks which are characterized by having uniform release points free from stresses induced in them as a result of installation or thermal stress forces, it is an object of the invention to provide an improved body containing a rupture disk.
Another object of the invention to provide a rupture disk which is attached by welding or brazing an enlarged ring supported on a reduced thickness or isolation portion of the body.
Yet another object of the invention to provide an anchor point for the rupture disk which is a ring of relatively massive or robust cross-section compared to the thinned or reduced cross-section of the isolating ring.
Still another object of the invention to provide a rupture disk held on a robust ring which is in turn attached to the remainder of the body by thinned, serpentine ring or other member of reduced cross-section.
A further object of the invention is to provide a rupture disk having a two-piece body with the two pieces being joined by welding or brazing at the interface of an axial flange on one portion of the body and a radial flange on the other portion of the body.
A still further object of the invention is to provide a two-piece body wherein the lower piece contains a small rib or the like to ensure precise seating of the cap or upper portion of the body prior to welding.
An additional object of the invention is to provide one or more methods of heat sinking for use in preventing undue thermal stresses from penetrating into the robust ring or other member on which the rupture disk is seated from an isolating ring of reduced thickness during welding or brazing of one-half of the body to the other half of the body.
Another object of the invention is to provide an auxiliary method of cooling which includes blowing air, and particularly highly moistened air, over the areas which are needed to be kept cooled so as to prevent undue heat transfer during welding or brazing of the upper portion of the body to the lower portion of the body.
Yet another object of the invention is to provide separate heat sinking mechanisms for the upper and lower portions of the body, with or without additional cooling of the temporary portion inserted into the lower half of the body.